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United States Patent | 5,081,397 |
Liang ,   et al. | January 14, 1992 |
A novel atmospheric pressure capacitively coupled ratio frequency plasma discharge method and apparatus. The apparatus is suitable for atomic absorption and atomic emission analysis of discrete sample volumes (1-50 .mu.l). The plasma can be operated at very low Radio Frequency (RF) input powers (10-600 W) which allow for optimal conditions for atom resonance line absorption measurements. Sample vaporization for analysis in the plasma is done by an electrically heated tantalum strip vaporizer. The vaporization and dissociation-atomization steps are separately controlled. Analyte absorption takes place in the plasma discharge which is characterized by a long path length (10-50 cm) and low support gas flow rate (0.05 to 6 L/m) both of which provide for a relatively long residence time. The device exhibits linear calibration plots and provides sensitivities in the range of from 3.5-40 pg.
Inventors: | Liang; Dong C. (Vancouver, CA); Blades; Michael W. (Surrey, CA) |
Assignee: | University of British Columbia (Vancouver, CA) |
Appl. No.: | 378263 |
Filed: | July 11, 1989 |
Current U.S. Class: | 315/111.21; 250/425; 313/231.31; 356/311; 356/316 |
Intern'l Class: | H01J 049/04 |
Field of Search: | 315/111.21 313/231.31 356/311,316 250/425 |
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4810933 | Mar., 1989 | Moisan et al. | 315/111. |
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TABLE I ______________________________________ Experimental Facilities and Operating Conditions ______________________________________ Plasma Power Supply System 1. Perkin-Elmer ICP 5500 System consisting of a Plasma-Therm (Kreeson, N.J.), HFP-2500F RF gener- ator, AMN-2500E automatic matching network, APCS-3 automatic power control system and PT - 2500 torch box. System 2. ENI Power Systems Inc. (Rochester, N.Y.) Model HPG-2 RF Power Supply. Frequency: 125 KHz- 375 KHz., Output Power: 0-200 W. Sample Vaporization Tantalum strip 1.5 cm by 0.5 cm with a depression at the center. Power: Varian Model CRA-61. Normal operat- ing cycle: Dry - 105 C for 60 s, Ash - 300-600 C for 15 s, Atomize - 2000- 3700 C for 2 s. Spectrometer Schoeffel-McPherson (Acton, MA) Model 270, 0.35 m Czerny-Turner mount scanning monochromator with 600 rulings/mm holographic grating. Reciprocal linear dispersion of 40 .degree.-A/ mm in the first order. Slits Entrance and exit slits set to 50 um for Mn determination, and 21 um for intensity ratio measurement. Hollow Cathode Lamps Hollow cathode lamps (HCL) were powered using a home-built, electron- ically modulated power supply. Modulation frequency - 250 Hz and a duty cycle of 50%. Normal operating currents were used for the lamps. Detector Electronics The photocurrent from a Hammatsu R955 photomultiplier tube was ampli- fied by a home-built preamplifier and fed to a Princeton Applied Research Model 121 Lock-In-Amplifier. The photomultiplier tube was powered using a McPherson Model EU-42A PMT powe supply. Data Acquisition Digital data acquisition was carried out using a Tulsa Computers (Owasso, OK) Telex Model 1280 IBM- At com- patible computer equipped with an RC Electronics (Santa Barbara, CA) Model ISC-16 analog-digital converter running the RC Computerscope software pack- age. Analog data was acquired using a Servocorder 210 chart recorder. ______________________________________
TABLE II __________________________________________________________________________ Sensitivies and Wavelengths for Ag, Cd, Cu, Li, B and Sb. Sensitivity (pg) Detection Limit (pg) Element Wavelength (nm) CCP-AAS GF-AAS[13] CCP-AES __________________________________________________________________________ Ag 328.1 10 5 0.7 Cd 228.8 3.5 1 0.7 Cu 324.8 40 30 Li 670.8 23 10 2 Sb 217.6 24 20 80 B 249.8 2000 1000 400 __________________________________________________________________________